The Effect of Wastewater Sludge Application on the Nitrogen Levels of Soil and Leachate

Abstract

Wastewater sludge has been already utilized in agricultural applications for several years as it represents an alternative source of nutrients for plant growth and an efficient soil conditioner enhancing certain physical properties of soil. However, the application of sewage sludge can lead to environmental or human health problems via leaching of nutrients, pathogens, heavy metals and organic compounds to groundwater. Particularly, nitrate is very soluble and it is generally considered by far the major, if not the only, N species leached when sewage sludge and manurial wastes are applied to land. In this study two different wastewater sludges (industry treatment plant and an urban wastewater treatment plant) were applied to soil columns at the dose of 50 ton ha^-1 and 150 ton ha^-1. After the artifical rainfall application, leachate was taken from the bottom of the columns and the variations of pH, EC_25°C, NH₄-N and NO₃-N were investigated. The results showed that the ammonium and nitrate nitrogen concentrations in leachates from sludge amended columns were similar to control values. At the end of the artifical rainfall period, pH and EC_25°C values were increased at the every sampling zone (0-15 cm, 15-30 cm, 30-45 cm) of amended column. The wastewater sludge application significantly increased the total nitrogen content of soil samples from each sampling zone. No nitrate nitrogen was determined in soils from amended columns, whereas ammonium nitrogen values were higher than control values. It is clear from the obtained data that nitrification was suppressed under the experimental conditions (accelerated rainfall simulation).